Signaling in wireless communication systems

ABSTRACT

A communication device includes an RF receiver that receives a combined signal including a first signal transmitted from a first node and a second signal transmitted from a second node, a channel estimator that estimates first channel information of the first signal and second channel information of the second signal, respectively, a multiuser detector that detects original signal values of the combined signal using the estimated first and second channel information and an RF transmitter that transmits a signal generated based on the values detected by the multiuser detector to the first node and the second node during a predetermined period.

BACKGROUND

Wireless communication systems are widely deployed to provide mobiledevices with various contents, such as voice, text, image, and movingpictures. For example, multiple channel access techniques allow multipleusers to share system resources, such as bandwidth and transmissionpower. Examples of multiple channel access techniques include codedivision multiple access (CDMA) systems, time division multiple access(TDMA) systems, frequency division multiple access (FDMA) systems, ororthogonal frequency division multiple access (OFDMA) systems. Suchmultiple channel access techniques can simultaneously supportcommunication between multiple mobile devices.

SUMMARY

Various embodiments of communication devices and communication methodsare disclosed herein. In one embodiment, a communication device includesan RF receiver that receives a combined signal including a first signaltransmitted from a first node and a second signal transmitted from asecond node, a channel estimator that estimates first channelinformation of the first signal and second channel information of thesecond signal, respectively, a multiuser detector that detects originalsignal values of the combined signal using the estimated first andsecond channel information, and an RF transmitter that transmits asignal generated based on the original signal values detected by themultiuser detector to the first node and the second node during apredetermined period.

In another embodiment, a communication method includes estimating firstchannel information of a first signal and second channel information ofa second signal transmitted simultaneously from different nodes,detecting original signal values of a combined signal including thefirst signal and the second signal based on the estimated first andsecond channel information by a multiuser detector, and transmitting asignal generated based on the detected original signal values to thedifferent nodes during a predetermined period.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows a schematic diagram of an illustrative embodiment of acommunication system.

FIG. 1B shows a schematic block diagram illustrating components of thecommunication devices of the communication system of FIG. 1A.

FIG. 2 shows a schematic diagram of symbol candidates of the signalreceived by the relay node shown in FIGS. 1A and 1B.

FIG. 3 shows a detailed block diagram of an illustrative embodiment ofthe relay node shown in FIGS. 1A and 1B.

FIG. 4 shows a detailed block diagram of another illustrative embodimentof the relay node shown in FIGS. 1A and 1B.

FIG. 5 is a flow diagram explaining an illustrative embodiment of acommunication method.

FIG. 6 is a flow diagram explaining another illustrative embodiment of acommunication method.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented herein. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe Figures, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

In one embodiment, the present disclosure provides a communicationdevice including a multiuser detector that detects values of a combinedsignal. The combined signal includes a first signal transmitted from afirst node and a second signal transmitted from a second node usingestimated first and second channel information.

FIG. 1A is a schematic diagram of an illustrative embodiment of acommunication system. FIG. 1B is a schematic block diagram illustratingcomponents of the communication devices of the communication system ofFIG. 1A. As depicted in FIG. 1A, a communication system 100 includesmultiple communication devices 110, 120 and 130. Each communicationdevice 110, 120 or 130 can transmit, receive or relay signals, and actas either a source node or a relay node. Various types of handheldcommunication apparatuses such as, but not limited to, mobile phones,smart phones or Personal Digital Assistants (PDAs) can be used forcommunication devices 110, 120 and 130. For the purpose of description,it is assumed hereinafter that communication devices 110 and 130 eachact as a source node (for example, first node 110 and second node 130),and communication device 120 acts as a relay node. However, one ofordinary skill in the art will appreciate that any of communicationdevices 110, 120 and 130 can act as a source node, a relay node, or acombination thereof.

As depicted in FIG. 1A, first node 110 and second node 130, as sourcenodes, substantially simultaneously transmit signals s₁ and s₃ to relaynode 120 during a time slot 1 (as depicted by a solid directional linein FIG. 1A). As used herein the time slot 1 can be defined as an uplinkslot during which signals s₁ and s₃ of first and second nodes 110 and130 are transmitted to relay node 120 based on a predeterminedcommunication protocol.

The transmitted first and second signals s₁ and s₃ are combined on aphysical layer such as, but not limited to, air interface, to generate acombined signal y₂. Combined signal y₂ is received at relay node 120.When combined signal y₂ is distorted after passing through multi pathfading channel, the original signal values of combined signal y₂ can bedetected by a multiuser detector 330 of relay node 120, which will befurther described in detail hereinafter. As used herein, the originalsignal values of combined signal y₂ refer to the values of combinedsignal y₂ in which no distortion is occurred. Relay node 120 thentransmits signal s₂ generated based on the detected original signalvalues of combined signal y₂ to first node 110 and second node 130during a time slot 2 (as depicted by a broken or dashed directional linein FIG. 1A). As used herein, the time slot 2 can be defined as adownlink slot during which signal s₂ is received at first and secondnodes 110 and 130 based on the predetermined communication protocol.

As depicted in FIG. 1B, first node 110 includes a first encoder 111, afirst decoder 113 and a first XOR (exclusive or) operator 115. Secondnode 130 includes a second encoder 131, a second decoder 133 and asecond XOR (exclusive or) operator 135.

First and second encoders 111 and 131 perform channel coding on signalss₁ and s₃ to generate encoded signals w₁ and w₃, respectively. In someembodiments, first and second encoders 111 and 131 perform the channelcoding by selectively inserting redundant bits into signals s₁ and s₃.By inserting redundant bits, bit errors of signals s₁ and s₃ can bedetected and corrected so that reliable signal transmission is achieved.First node 110 and second node 130 transmit encoded signals w₁ and w₃,respectively, for reception by relay node 120. Prior to reception byrelay node 120, encoded signals w₁ and w₃ are combined on a physicallayer, such as an air interface.

Relay node 120 receives combined signal y₂ including encoded signals w₁and w₃. Further, relay node 120 detects original signal values ofcombined signal y₂ using multiuser detector 330 and generates signal s₂using the original signal values, which will be further describedhereinafter. Relay node 120 transmits signal s₂ to both first node 110and second node 130.

First decoder 113 of first node 110 decodes signal s₂ and second decoder133 of second node 130 decodes signal s₂. First and second decoders 113and 133 provide decoded signal ŝ₂ to first and second XOR operators 115and 135, respectively.

First XOR operator 115 of first node 110 performs an XOR operation ondecoded signal ŝ₂ and first signal s₁ to generate second signal s₃ thathas been transmitted from second node 130. Since decoded signal ŝ₂ isthe decoded signal of signal s₂ which is generated using combined signaly₂, it includes first signal s₁ and second signal s₃. Thus, first node110 can receive second signal s₃ transmitted from second node 130 usingthe XOR operation.

Second XOR operator 135 of second node 130 performs an XOR operation ondecoded signal ŝ₂ and second signal s₃ to generate first signal s₁ thathas been transmitted from first node 110. Since decoded signal ŝ₂includes first signal s₁ and second signal s₃, as described above,second node 130 can receive first signal s₁ using the XOR operation.

In the illustrative embodiment, signals (for example, signal s₁ andsignal s₃) can be transmitted and received between first and secondnodes 110 and 130 which are far away from each other during relativelyshort time periods, for example, two time slots (for example, time slots1 and 2).

In the above-stated illustrative embodiment, the channel codes used byencoders 111 and 131 and decoders 113 and 133 have linearity. Forexample, the channel codes may include Linear Block Codes, such asHamming codes, Golay codes, BCH codes, Reed Solomon codes and (Linear)Convolution Codes. However, the channel codes used by encoders 111 and131 and decoders 113 and 133 are not limited thereto and any channelcode having linearity may be employed.

FIG. 2 is a schematic diagram of symbol candidates of a signal receivedby the relay node of FIGS. 1A and 1B. A combined signal includingmultiple signals is expressed with information of signals eachtransmitted from a multiple number of nodes and channel information ofthe transmitted signals. The channel information includes a channelcoefficient of an ith node at a certain time slot and an averagereceived power level at the ith node. By way of example, but notlimitation, the channel coefficient may be an independent andidentically-distributed (i.i.d.) complex Gaussian random variable withvariance one (1). Further, noise is added to the combined signal. Thenoise may be Additive White Gaussian Noise (AWGN) whose power spectraldensity is N₀, but the noise is not limited thereto.

For example, the combined signal received by relay node 120 (see FIG.1A) is expressed by Equation 1 as follows.y ₂ =h ₁√{square root over (P ₁)}x ₁ +h ₃√{square root over (P ₃)}x ₃+n  [Equation 1]Here, x₁ denotes a symbol value of first signal s₁ transmitted fromfirst node 110 (see FIG. 1A), x₃ denotes a symbol value of second signals₃ transmitted from second node 130 (see FIG. 1A) and y₂ denotes thecombined signal received by relay node 120. Further, h₁ and h₃respectively denote channel coefficients of first signal s₁ and secondsignal s₃, and P₁ and P₃ respectively denote average received powerlevels at first node 110 and second node 130. Furthermore, n denotesAdditive White Gaussian Noise (AWGN) added to first signal s₁ and secondsignal s₃.

For example, if first node 110 and second node 130 transmit BPSK (BinaryPhase Shift Keying) modulated signals, symbol values x₁ and x₃ are minusone (−1) or one (1). Accordingly, combined signal y₂ has four possiblesymbol candidates as expressed in the following Equation 2.C ₀₀ =h ₁√{square root over (P ₁)}+h ₃√{square root over (P ₃)}, C ₁₀=−h ₁√{square root over (P ₁)}+h ₃√{square root over (P ₃)},C ₁₁ =−h ₁√{square root over (P ₁)}−h ₃√{square root over (P ₃)}, C ₀₁=h ₁√{square root over (P ₁)}−h ₃√{square root over (P ₃)}  [Equation 2]

In Equation 2, C₀₀ is a possible symbol candidate when symbol value x₁of first signal s₁ is one (1) and symbol value x₃ of second signal s₃ isone (1). C₁₀ is a possible symbol candidate when symbol value x₁ offirst signal s₁ is minus one (−1) and symbol value x₃ of second signals₃ is one (1). C₁₁ is a possible symbol candidate when symbol value x₁of first signal s₁ is minus one (−1) and symbol value x₃ of secondsignal s₃ is minus one (−1). C₀₁ is a possible symbol candidate whensymbol value x₁ of first signal s₁ is one (1) and symbol value x₃ ofsecond signal s₃ is minus one (−1).

Referring to FIG. 2 and Equation 2, combined signal y₂ is determined asone (1) if the symbol of combined signal y₂ is detected as C₁₀ or C₀₁.Further, combined signal y₂ is determined as zero (0) if the symbol ofcombined signal y₂ is detected as C₀₀ or C₁₁. Since, first signal s₁ andsecond signal s₃ are combined during time slot 1 (as depicted by a solidarrow in FIG. 1A), symbol value x₁ of first signal s₁ and symbol valuex₃ of second signal s₃ are XOR operated each other. Accordingly, ifsymbol value x₁ and x₃ are the same, combined signal y₂ is one (1) andif symbol value x₁ and x₃ are different, combined signal y₂ is zero (0).

Although the BPSK modulation signals have been illustrated above, itwill be apparent to those skilled in the art that any modulation method,such as M-QAM (Quadrature Amplitude Modulation) method can also be used.

FIG. 3 is a detailed block diagram of an illustrative embodiment of therelay node shown in FIGS. 1A and 1B. In the illustrative embodiment,relay node 120 includes an RF (Radio Frequency) receiver 310, a channelestimator 320, a multiuser detector 330, a decoder 340 (optional), anencoder 350 (optional) and an RF transmitter 360.

RF receiver 310 receives combined signal y₂ including first signal s₁transmitted from first node 110 (see FIG. 1A) and second signal s₃transmitted from second node 130 (see FIG. 1A) during time slot 1 (asdepicted by a solid directional line in FIG. 3). As discussed, firstsignal s₁ and second signal s₃ may be encoded signals and they can becombined on a physical layer. RF receiver 310 provides combined signaly₂ to multiuser detector 330. Further, RF receiver 310 receives firstand second pilot signals (not shown) from first and second nodes 110 and130 and provides the received first and second pilot signals to channelestimator 320.

Channel estimator 320 estimates channel information including a receivedpower level and a channel coefficient by using the first and secondpilot signals received by RF receiver 310. For example, channelestimator 320 estimates first channel information including a firstreceived power level and a first channel coefficient of first signal s₁by using the first pilot signal transmitted from first node 110 throughRF receiver 310. Further, channel estimator 320 estimates second channelinformation including a second received power level and a second channelcoefficient of second signal s₃ by using the second pilot signaltransmitted from second node 130 through RF receiver 310. Then, channelestimator 320 provides the estimated first and second channelinformation to multiuser detector 330.

Multiuser detector 330 detects original signal values of combined signaly₂ received from RF receiver 310 using the estimated first and secondchannel information received from channel estimator 320. The valuesdetected by multiuser detector 330 may be, but not limited to, one (1)or zero (0), and can be varied depending on a modulation method.

Multiuser detector 330 employs various detecting methods such as, butnot limited to, a joint ML (maximum likelihood) detecting method and anyother multiuser detecting method.

To detect the original signal values of combined signal y₂, multiuserdetector 330 is configured to execute LLR (log likelihood ratio)computation of combined signal y₂. For example, if BPSK is used as amodulation method, the LLR (log likelihood ratio) value is calculated byEquation 3 as follows.

$\begin{matrix}\begin{matrix}{\Lambda_{s_{2}} = {\log\frac{P\left( {s_{2} = {0❘y_{2}}} \right)}{P\left( {s_{2} = {1❘y_{2}}} \right)}}} \\{{= {\log\frac{{P\left( {{s_{1} = 0},{s_{3} = {0❘y_{2}}}} \right)} + {P\left( {{s_{1} = 1},{s_{3} = {1❘y_{2}}}} \right)}}{{P\left( {{s_{1} = 1},{s_{3} = {0❘y_{2}}}} \right)} + {P\left( {{s_{1} = 0},{s_{3} = {1❘y_{2}}}} \right)}}}},}\end{matrix} & \left\lbrack {{Equation}\mspace{11mu} 3} \right\rbrack\end{matrix}$Here, Λ_(s2) denotes the LLR (log likelihood ratio) value, and P(A)denotes a probability of occurrence of an event A. For example, P(s₁=0,s₃=0|y₂) is a probability of occurrence of an event in which, whencombined signal y₂ is received, the values of first signal s₁ and secondsignal s₃ are zero (0), respectively. If Λ_(s2) is equal to or less thanzero (0), the original signal value of combined signal y₂ is determinedas one (1). If Λ_(s2) is larger than zero (0), the original signal valueof combined signal y₂ is determined as zero (0).

Further, assuming that a first probability (the value of first signal s₁is zero (0)) and a second probability (the value of first signal s₁ isone (1)) are equal; and that a third probability (the value of secondsignal s₃ is zero (0)) and a fourth probability (the value of secondsignal s₃ is one (1)) are equal, Equation 3 is expressed by thefollowing Equation 4 according to Bayes' rule.

$\begin{matrix}\begin{matrix}{\Lambda_{S_{2}} = {\log\frac{{p\left( {{{y_{2}❘s_{1}} = 0},{s_{3} = 0}} \right)} + {p\left( {{{y_{2}❘s_{1}} = 1},{s_{3} = 1}} \right)}}{{p\left( {{{y_{2}❘s_{1}} = 1},{s_{3} = 0}} \right)} + {p\left( {{{y_{2}❘s_{1}} = 0},{s_{3} = 1}} \right)}}}} \\{{= {\log\frac{{\exp\left( {- \frac{{{y_{2} - C_{00}}}^{2}}{2\sigma^{2}}} \right)} + {\exp\left( {- \frac{{{y_{2} - C_{11}}}^{2}}{2\sigma^{2}}} \right)}}{{\exp\left( {- \frac{{{y_{2} - C_{10}}}^{2}}{2\sigma^{2}}} \right)} + {\exp\left( {- \frac{{{y_{2} - C_{01}}}^{2}}{2\sigma^{2}}} \right)}}}},}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$Here, p(α) denotes a probability density function of α. For example,p(y₂|s₁=0, s₃=0) is a probability density function of combined signal y₂when the value of first signal s₁ is zero (0) and the value of secondsignal s₃ is zero (0). σ² denotes a variance, and C₀₀, C₀₁, C₁₀ and C₁₁denote the symbol candidates of combined signal y₂ as expressed inEquation 2, respectively.

Multiuser detector 330 produces a vector L₂ composed of the valuesdetected as a result of the LLR (log likelihood ratio) computation andprovides vector L₂ to decoder 340.

Although relay node 120 has been described to execute the LLR (loglikelihood ratio) computation on BPSK modulated signals, it will beapparent to those skilled in the art that the LLR (log likelihood ratio)computation can also be applied to another signals modulated by anothermodulation method, such as M-QAM.

As described above, multiuser detector 330 produces vector L₂ with amultiuser detecting method, such as a joint ML (maximum likelihood)detecting method. Therefore, relay node 120 can decrease multi pathfading even if a pre-equalizer, which is used to compensate the multipath fading, is not provided.

Decoder 340 receives vector L₂ having the LLR (log likelihood ratio)values and decodes vector L₂ using a first channel code to generatedecoded vector ŝ₂. Further, decoder 340 provides decoded vector ŝ₂ toencoder 350.

Encoder 350 receives decoded vector ŝ₂ from decoder 340 and encodesdecoded vector ŝ₂ using a second channel code to generate an encodedvector ŵ′₂. Then, encoder 350 provides encoded vector ŵ′₂ to RFtransmitter 360. As previously described, the first and second channelcodes have linearity, and various channel codes having linearity can beused for the first and second channel codes.

RF transmitter 360 modulates encoded vector ŵ′₂ into signal s₂ andtransmits signal s₂ to first node 110 and second node 130 during timeslot 2 (as depicted by a broken arrow in FIG. 3).

In another embodiment, relay node 120 is configured without decoder 340and encoder 350. Since decoder 340 and encoder 350 are omitted, thedecoding and encoding of vector L₂ are also omitted in this embodiment.Particularly, in response to combined signal y₂ transmitted from RFreceiver 310 and the first and second channel information estimated bychannel estimator 320, multiuser detector 330 generates vector L₂, andprovide it to RF transmitter 360. In response to vector L₂, RFtransmitter 360 generates signal s₂ without the above-mentioned decodingand encoding processes, and transmits generated signal s₂ to first andsecond nodes 110 and 130. First node 110 and second node 130 decodessignal s₂ using decoder 113 and 133 (See FIG. 1B) as discussedpreviously.

Accordingly, first and second nodes 110 and 130 obtain signals s₃ and s₁respectively by XOR operations of the decoded signals of signal s₂ andtheir own signals s₁ and s₃. Since all of the channel codes used byfirst and second nodes 110 and 130, decoder 340 and encoder 350 havelinearity, the decoded signals of signal s₂ satisfies linearity withrespect to signals s₁ and s₃ and signals s₁ and s₃ can be obtainedrespectively by the XOR operation.

FIG. 4 is a detailed block diagram of another illustrative embodiment ofthe relay node shown in FIGS. 1A and 1B. In this embodiment, a relaynode 400 includes an RF (Radio Frequency) receiver 410, a channelestimator 420, a multiuser detector 430, a first decoder 440, a seconddecoder 450, an XOR operator 460, an encoder 470 and an RF transmitter480. Since the function and operation of RF receiver 410, channelestimator 420, encoder 470 and RF transmitter 480 in FIG. 4 aresubstantially identical or similar to those of RF receiver 310, channelestimator 320, encoder 350 and RF transmitter 360 respectively in FIG.3, redundant description thereof will be omitted herein.

Relay node 400 includes two decoders (for example, first decoder 440 andsecond decoder 450), while relay node 120 depicted in FIG. 3 includesone decoder 340. Further, relay node 400 includes XOR operator 460 inassociation with first and second decoders 440 and 450.

As in relay node 120 depicted in FIG. 3, multiuser detector 430 receivescombined signal y₂ from RF receiver 410 and estimated first and secondchannel information from channel estimator 420. While multiuser detector330 depicted in FIG. 3 detects original signal values of combined signaly₂, multiuser detector 430 depicted in FIG. 4 detects the values offirst signal s₁ and second signal s₃ respectively from combined signaly₂. Then, the original signal values of combined signal y₂ are generatedusing the detected values of first signal s₁ and second signal s₃.Specifically, multiuser detector 430 detects values of first signal s₁based on first channel information and second channel informationestimated by channel estimator 420. Further, multiuser detector 430detects values of second signal s₃ based on the first channelinformation and the second channel information. At this time, the valuesdetected by multiuser detector 430 may be, but not limited to, one (1)or zero (0), and can be varied depending on the modulation method.Furthermore, multiuser detector 430 generates two vectors (first andsecond vectors L₁ and L₃) for first and second signals s₁ and s₃,respectively.

Particularly, multiuser detector 430 executes LLR (log likelihood ratio)computation of first signal s₁ and second signal s₃. For example, ifBPSK is used as a modulation method, the LLR (log likelihood ratio)value of first signal s₁ is expressed by the following Equation 5.

$\begin{matrix}{\Lambda_{s_{1}} = {\log\frac{{P\left( {{s_{1} = 0},{s_{3} = {0❘y_{2}}}} \right)} + {P\left( {{s_{1} = 0},{s_{3} = {1❘y_{2}}}} \right)}}{{P\left( {{s_{1} = 1},{s_{3} = {0❘y_{2}}}} \right)} + {P\left( {{s_{1} = 1},{s_{3} = {1❘y_{2}}}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$Further, the LLR (log likelihood ratio) value of second signal s₃ isexpressed by the following Equation 6.

$\begin{matrix}{\Lambda_{s_{3}} = {\log\frac{{P\left( {{s_{1} = 0},{s_{3} = {0❘y_{2}}}} \right)} + {P\left( {{s_{1} = 1},{s_{3} = {0❘y_{2}}}} \right)}}{{P\left( {{s_{1} = 0},{s_{3} = {1❘y_{2}}}} \right)} + {P\left( {{s_{1} = 1},{s_{3} = {1❘y_{2}}}} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$In Equations 5 and 6, P(A) denotes a probability of occurrence of anevent A. For example, P(s₁=0, s₃=0|y₂) is a probability of occurrence ofan event in which, when combined signal y₂ is received, the values offirst signal s₁ and second signal s₃ are respectively zero (0). If theLLR (log likelihood ratio) Λ_(s1) or Λ_(s3) is equal to or less thanzero (0), the value of first signal s₁ or second signal s₃ is determinedas one (1). If Λ_(s1) or Λ_(s3) is larger than zero (0), the value offirst signal s₁ or second signal s₃ is determined as zero (0).

Further, multiuser detector 430 produces a first vector L₁ composed ofthe LLR (log likelihood ratio) values of first signal s₁ and providesfirst vector L₁ to first decoder 440. Furthermore, multiuser detector430 produces a second vector L₃ composed of the LLR (log likelihoodratio) values of second signal s₃ and provides second vector L₃ tosecond decoder 450.

First decoder 440 receives first vector L₁ composed of the LLR (loglikelihood ratio) values of first signal s₁ and decodes first vector L₁using a first channel code. Further, first decoder 440 provides adecoded vector ŝ₁ to XOR operator 460.

Second decoder 450 receives second vector L₃ composed of the LLR (loglikelihood ratio) values of second signal s₃ and decodes second vectorL₃ using a second channel code. Further, second decoder 450 provides adecoded vector ŝ₃ to XOR operator 460.

XOR operator 460 performs an XOR operation on decoded vector ŝ₁ anddecoded vector ŝ₃. Accordingly, XOR operator 460 generates a combinedvector ŝ₂ and then provides combined vector ŝ₂ to encoder 470.

Encoder 470 encodes combined vector ŝ₂ using a third channel code andthen transmits an encoded vector ŵ′₂ to RF transmitter 480. RFtransmitter 480 modulates encoded vector ŵ′₂ into signal s₂ andtransmits signal s₂ to both first node 110 (see FIG. 1A) and second node130 (see FIG. 1A). As described previously, the first, second and thirdchannel codes have linearity, and various channel codes having linearitycan be used for the first, second and third channel codes.

Although first decoder 440, second decoder 450 and encoder 470 are shownin FIG. 4, they are optional and may be omitted in certain embodiments.In an example embodiment in which relay node 400 is configured withoutfirst decoder 440, second decoder 450 and encoder 470, XOR operator 460performs an XOR operation directly on first vector L₁ and second vectorL₃, each received from multiuser detector 430, and RF transmitter 480transmits a signal generated by the XOR-operation without theabove-mentioned decoding and encoding processes.

FIG. 5 is a flow diagram explaining an illustrative embodiment of acommunication method. Referring to FIGS. 1A, 1B, 3 and 5, an exampleembodiment of a communication method is illustrated. A signal (forexample, a combined signal y₂) is received in a communication device(for example, relay node 120) during a certain time period (for example,time slot 1) (Operation 510). The signal includes two encoded signals(for example, first signal s₁ transmitted from first node 110 and secondsignal s₃ transmitted from second node 130, which is combined on aphysical layer).

Channel information is estimated by using a pilot signal received by RFreceiver 310 (Operation 520). The channel information includes areceived power level and a channel coefficient. For example, firstchannel information is estimated using a first pilot signal transmittedfrom first node 110. The first channel information includes a firstreceived power level and a first channel coefficient of first signal s₁.Further, second channel information is estimated using a second pilotsignal transmitted from second node 130. The second channel informationincludes a second received power level and a second channel coefficientof second signal s₃.

Original signal values of combined signal y₂ received in operation 510are detected using the first and second channel information estimated inoperation 520 (Operation 530). Further, vector L₂ composed of theoriginal signal values is produced by executing LLR (log likelihoodratio) computation (Operation 530). The values detected in operation 530may be, but not limited to, one (1) or zero (0), and can be varieddepending on the modulation method. Since the detailed process fordetecting the original signal values of combined signal y₂ has alreadybeen discussed with reference to FIG. 3, redundant description thereofwill be omitted herein.

Vector L₂ is decoded using a first channel code to generate vector ŝ₂(Operation 540). Vector ŝ₂ decoded in operation 540 is encoded using asecond channel code to generate vector ŵ′₂ (Operation 550). Vector ŵ′₂encoded in operation 550 is modulated into signal s₂ and signal s₂ istransmitted to first node 110 and second node 130 during a predeterminedperiod (for example, time slot 2) (Operation 560).

Signal s₂ is decoded into decoded vector ŝ₂ at first node 110 and firstnode 110 performs XOR-operation on decoded vector ŝ₂ and signal s₁ toobtain or generate second signal s₃ that has been transmitted fromsecond node 130. Further, signal s₂ is decoded into decoded vector ŝ₂ atsecond node 130 and second node 130 performs XOR-operation on decodedvector ŝ₂ and signal s₃ to obtain or generate first signal s₁ that hasbeen transmitted from first node 110.

FIG. 6 is a flow diagram explaining another illustrative embodiment of acommunication method. Referring to FIGS. 1A, 1B, 4 and 6, an exampleembodiment of a communication method is illustrated. Since the functionand process of operation 610 and 620 in FIG. 6 may be similar to thoseof operation 510 and 520 respectively in FIG. 5, redundant descriptionthereof will be omitted herein.

As compared to operation 530 in FIG. 5 in which the values of onecombined signal y₂ are detected, the values of two signals (first signals₁ and second signal s₃) are detected, respectively (Operation 630). Thevalues of first signal s₁ are detected using first channel informationand second channel information estimated in operation 620 and the valuesof second signal s₃ are detected using the first channel information andthe second channel information estimated in operation 620. The values offirst signal s₁ and second signal s₃ can be detected using, but notlimited to, LLR (log likelihood ratio) computation of first signal s₁and second signal s₃, respectively. Since the detailed process fordetecting the values of first signal s₁ and values of second signal s₃is already discussed with reference to FIG. 4, redundant descriptionthereof will be omitted herein.

Further, first vector L₁ is produced by executing LLR (log likelihoodratio) computation of first signal s₁ and second vector L₃ is producedby executing LLR (log likelihood ratio) computation of second signal s₃,respectively (Operation 640). The detected values may be, but notlimited to, one (1) or zero (0), and can be varied depending on themodulation method.

First vector L₁ is decoded using a first channel code and second vectorL₃ is decoded using a second channel code (Operation 650). Accordingly,decoded vectors ŝ₁ and ŝ₃ are generated.

An XOR operation is performed on decoded vectors ŝ₁ and ŝ₃ and thuscombined vector ŝ₂ is generated (Operation 660). Then, combined vectorŝ₂ is encoded to generate vector ŵ′₂ using a third channel code(Operation 670). Encoded vector ŵ′₂ is modulated into signal s₂ andsignal s₂ is transmitted to both first node 110 and second node 130during a predetermined period (for example, time slot 2) (Operation680).

One skilled in the art will appreciate that, for this and otherprocesses and methods disclosed herein, the functions performed in theprocesses and methods may be implemented in differing order.Furthermore, the outlined steps and operations are only provided asexamples, and some of the steps and operations may be optional, combinedinto fewer steps and operations, or expanded into additional steps andoperations without detracting from the essence of the disclosedembodiments.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, reagents, compounds compositions or biological systems, whichcan, of course, vary. It is also to be understood that the terminologyused herein is for the purpose of describing particular embodimentsonly, and is not intended to be limiting.

In an illustrative embodiment, any of the operations, processes, etc.described herein can be implemented as computer-readable instructionsstored on a computer-readable medium. The computer-readable instructionscan be executed by a processor of a mobile unit, a network element,and/or any other computing device.

There is little distinction left between hardware and softwareimplementations of aspects of systems; the use of hardware or softwareis generally (but not always, in that in certain contexts the choicebetween hardware and software can become significant) a design choicerepresenting cost vs. efficiency tradeoffs. There are various vehiclesby which processes and/or systems and/or other technologies describedherein can be effected (e.g., hardware, software, and/or firmware), andthat the preferred vehicle will vary with the context in which theprocesses and/or systems and/or other technologies are deployed. Forexample, if an implementer determines that speed and accuracy areparamount, the implementer may opt for a mainly hardware and/or firmwarevehicle; if flexibility is paramount, the implementer may opt for amainly software implementation; or, yet again alternatively, theimplementer may opt for some combination of hardware, software, and/orfirmware.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples. Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/or operations, it will beunderstood by those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof. In one embodiment,several portions of the subject matter described herein may beimplemented via Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), digital signal processors (DSPs), orother integrated formats. However, those skilled in the art willrecognize that some aspects of the embodiments disclosed herein, inwhole or in part, can be equivalently implemented in integratedcircuits, as one or more computer programs running on one or morecomputers (e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g., as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and or firmwarewould be well within the skill of one of skill in the art in light ofthis disclosure. In addition, those skilled in the art will appreciatethat the mechanisms of the subject matter described herein are capableof being distributed as a program product in a variety of forms, andthat an illustrative embodiment of the subject matter described hereinapplies regardless of the particular type of signal bearing medium usedto actually carry out the distribution. Examples of a signal bearingmedium include, but are not limited to, the following: a recordable typemedium such as a floppy disk, a hard disk drive, a CD, a DVD, a digitaltape, a computer memory, etc.; and a transmission type medium such as adigital and/or an analog communication medium (e.g., a fiber opticcable, a waveguide, a wired communications link, a wirelesscommunication link, etc.).

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use engineering practices to integrate such describeddevices and/or processes into data processing systems. That is, at leasta portion of the devices and/or processes described herein can beintegrated into a data processing system via a reasonable amount ofexperimentation. Those having skill in the art will recognize that atypical data processing system generally includes one or more of asystem unit housing, a video display device, a memory such as volatileand non-volatile memory, processors such as microprocessors and digitalsignal processors, computational entities such as operating systems,drivers, graphical user interfaces, and applications programs, one ormore interaction devices, such as a touch pad or screen, and/or controlsystems including feedback loops and control motors (e.g., feedback forsensing position and/or velocity; control motors for moving and/oradjusting components and/or quantities). A typical data processingsystem may be implemented utilizing any suitable commercially availablecomponents, such as those typically found in datacomputing/communication and/or network computing/communication systems.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a second third, middle third and firstthird, etc. As will also be understood by one skilled in the art alllanguage such as “up to,” “at least,” and the like include the numberrecited and refer to ranges which can be subsequently broken down intosubranges as discussed above. Finally, as will be understood by oneskilled in the art, a range includes each individual member. Thus, forexample, a group having 1-3 cells refers to groups having 1, 2, or 3cells. Similarly, a group having 1-5 cells refers to groups having 1, 2,3, 4, or 5 cells, and so forth.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. A communication device comprising: an RF receiverthat receives a combined signal including a first signal transmittedfrom a first node and a second signal transmitted from a second node; achannel estimator that estimates first channel information of the firstsignal using a first pilot signal and estimates second channelinformation of the second signal using a second pilot signal; amultiuser detector that detects original signal values of the combinedsignal using the estimated first and second channel information; an RFtransmitter that transmits a third signal generated based on thedetected original signal values to the first node and the second nodeduring a predetermined period; a decoder that decodes a vector composedof the original signal values detected by the multiuser detector using afirst channel code; and an encoder that encodes the decoded vector usinga second channel code.
 2. The communication device of claim 1, whereinthe multiuser detector is a joint-ML (maximum likelihood) detector. 3.The communication device of claim 1, wherein the first channel code andthe second channel code have linearity.
 4. The communication device ofclaim 1, wherein the multiuser detector is configured to execute LLR(log likelihood ratio) computation of the combined signal.
 5. Thecommunication device of claim 1, wherein the first channel informationincludes a received power level and a channel coefficient of the firstsignal, and the second channel information includes a received powerlevel and a channel coefficient of the second signal.
 6. A communicationdevice comprising: an RF receiver for receiving a combined signalincluding a first signal transmitted from a first node and a secondsignal transmitted from a second node; a channel estimator forestimating first channel information of the first signal and estimatingsecond channel information of the second signal; a multiuser detectorfor detecting, from the combined signal, values of the first signalusing the estimated first channel information, and detecting, from thecombined signal, values of the second signal using the estimated secondchannel information, the values of the second signal being determinedseparately from the values of the first signal; an XOR (exclusive-or)operator for performing an XOR-operation on the values of the firstsignal and the values of the second signal; and an RF transmitter fortransmitting a third signal generated based on the XOR-operation to thefirst node and the second node during a predetermined period.
 7. Thecommunication device of claim 6, wherein the multiuser detector is ajoint-ML (maximum likelihood) detector.
 8. The communication device ofclaim 6, further comprising: a first decoder for decoding a first vectorcomposed of the detected values of the first signal using a firstchannel code; a second decoder for decoding a second vector composed ofthe detected values of the second signal using a second channel code;and an encoder for encoding the XOR-operated values using a thirdchannel code wherein the XOR operator performs the XOR-operation on thedecoded first vector and the decoded second vector.
 9. The communicationdevice of claim 8, wherein the first channel code, the second channelcode and the third channel code have linearity.
 10. The communicationdevice of claim 8, wherein the multiuser detector is configured toexecute LLR (log likelihood ratio) computation of the first signal andthe second signal.
 11. The communication device of claim 8, wherein thefirst channel information includes a received power level and a channelcoefficient of the first signal, and the second channel informationincludes a received power level and a channel coefficient of the secondsignal.
 12. A communication method comprising: receiving a combinedsignal including a first signal and a second signal transmittedsubstantially simultaneously from different nodes; estimating firstchannel information of the first signal and second channel informationof the second signal; detecting original signal values of the firstsignal from the combined signal based on the estimated first channelinformation, and detecting original signal values of the second signalfrom the combined signal based on the estimated second channelinformation, wherein the original signal values of the first signal andthe second signal are independently detected by a multiuser detectingmethod; performing an XOR (exclusive-or)-operation on the detectedvalues of the first signal and the detected values of the second signal;and transmitting a third signal generated based on the XOR- operation tothe first and second nodes during a predetermined period.
 13. Thecommunication method of claim 12, wherein the multiuser detecting methodis a joint-ML (maximum likelihood) detecting method.
 14. Thecommunication method of claim 12, further comprising: decoding a firstvector composed of the detected original signal values of the firstsignal using a first channel code; and decoding a second vector composedof the detected original signal values of the second signal using asecond channel code, wherein the XOR-operation is performed on thedecoded first and second vectors to generate a third vector.
 15. Thecommunication method of claim 14, further comprising: encoding the thirdvector generated by the XOR-operation by using a third channel code. 16.The communication method of claim 15, wherein the multiuser detectingmethod is a LLR (log likelihood ratio) detecting method.
 17. Thecommunication method of claim 15, wherein the first channel code, thesecond channel code, and the third channel code have linearity.
 18. Thecommunication method of claim 12, wherein the estimated first channelinformation includes a received power level and a channel coefficient ofthe first signal, and the second channel information includes a receivedpower level and a channel coefficient of the second signal.
 19. Thecommunication method of claim 12, wherein the estimated first channelinformation is estimated using a first pilot signal and the estimatedsecond channel information is estimated using a second pilot signal.